IV Clinical Correlations

C H A P T E R 1 6

Basal Nuclei and

Extrapyramidal Motor

System

Objectives

1.List the components of the basal nuclei.

2.Define striatum, corpus striatum, and claustrum.

3.Describe the anatomical structures that make up the extrapyramidal system and outline their functions.

4.Describe the anatomy, clinical signs, and treatment of Parkinson Disease, Huntington Disease, hemiballism, Wilson Disease, and tardive dyskinesia.

IBasal Nuclei (Ganglia) (Figure 16-1)

A.Components

1.Caudate nucleus

2.Putamen

3.Globus pallidus

B.Grouping of the Basal Nuclei

1.The striatum consists of the caudate nucleus and putamen.

2.The lentiform nucleus consists of the globus pallidus and putamen.

3.The corpus striatum consists of the lentiform nucleus and caudate nucleus.

4.The claustrum lies between the lentiform nucleus and the insular cortex. It has reciprocal connections between the sensory cortices (i.e., visual cortex) (Figures 16-2 to 16-4).

II The Extrapyramidal (Striatal) Motor System (see Figure 16-1)

plays a role in the initiation and execution of somatic motor activity, especially willed movement. It is also involved in automatic stereotyped postural and reflex motor activity (e.g., normal subjects swing their arms when they walk).

A.Structure. The striatal motor system includes the following structures:

1.Neocortex

2.Striatum (caudatoputamen or neostriatum)

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Figure 16-1 Coronal section through the midthalamus at the level of the mammillary bodies. The basal nuclei (ganglia) are all prominent at this level and include the striatum and lentiform nucleus. The subthalamic nucleus and substantia nigra are important components of the striatal motor system. CM, centromedian nucleus; VA, ventral anterior nucleus; VL, ventral lateral nucleus.

3.Globus pallidus

4.Subthalamic nucleus

5.Substantia nigra (i.e., pars compacta and pars reticularis)

6.Thalamus (ventral anterior, ventral lateral, and centromedian nuclei)

B.Figure 16-5 shows the major afferent and efferent connections of the striatal system.

C.Neurotransmitters are seen in Figure 16-6.

IIIClinical Correlation

A.Parkinson Disease. This is a degenerative disease that affects the substantia nigra and its projections to the striatum.

1.Results of Parkinson disease are a depletion of dopamine in the substantia nigra and striatum as well as a loss of melanin-containing dopaminergic neurons in the substantia nigra.

2.Clinical signs are bradykinesia, stooped posture, shuffling gait, cogwheel rigidity, pill-rolling tremor, and masked facies. Lewy bodies are found in the melanin-containing neurons of the substantia nigra. Progressive supranuclear palsy is associated with Parkinson disease.

3.Treatment has been successful with L-dopa. Surgical intervention includes pallidotomy (rigidity) and ventral thalamotomy (tremor).

Figure 16-3 An axial (horizontal) section through the anterior commissure and the massa intermedia.

F. Hepatolenticular Degeneration (Wilson Disease) is an autosomal recessive disorder that is caused by a defect in the metabolism of copper. The gene locus is on chromosome 13.

1.Clinical signs include choreiform or athetotic movements, rigidity, and wing-beating tremor. Tremor is the most common neurologic sign.

2.Lesions are found in the lentiform nucleus. Copper deposition in the limbus of the cornea gives rise to the corneal Kayser–Fleischer ring, which is a pathognomonic sign. Deposition of copper in the liver leads to multilobular cirrhosis.

3.Psychiatric symptoms include psychosis, personality disorders, and dementia.

4.The diagnosis is based on low serum ceruloplasmin, elevated urinary excretion of copper, and increased copper concentration in a liver biopsy specimen.

5.Treatment includes penicillamine, a chelator.

G.Tardive Dyskinesia is a syndrome of repetitive choreic movement that affects the face and trunk. It results from treatment with phenothiazines, butyrophenones, or metoclopramide.

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Figure 16-4 A coronal section through the lentiform nucleus and the amygdaloid nucleus; the lentiform nucleus consists of the putamen and the globus pallidus; the amygdaloid nucleus appears as a circular profile below the uncus.

Brain stem and spinal cord

Figure 16-5 Major afferent and efferent connections of the striatal system. The striatum receives major input from three sources: the thalamus, neocortex, and substantia nigra. The striatum projects to the globus pallidus and substantia nigra. The globus pallidus is the effector nucleus of the striatal system; it projects to the thalamus and subthalamic nucleus. The substantia nigra also projects to the thalamus. The striatal motor system is expressed through the corticonuclear and corticospinal tracts. CM, centromedian nucleus; GABA, γ-aminobutyric acid; VA, ventral anterior nucleus; VL, ventral lateral nucleus.

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Figure 16-6 Major neurotransmitters of the extrapyramidal motor system. Within the striatum, globus pallidus, and pars reticularis of the substantia nigra (S. nigra), γ-aminobutyric acid (GABA) is the predominant neurotransmitter. GABA may coexist in the same neuron with enkephalin (ENK) or substance P (SP). Dopamine-containing neurons are found in the pars compacta of the substantia nigra. Acetylcholine (ACh) is found in the local circuit neurons of the striatum. The subthalamic nucleus projects excitatory glutaminergic fibers to the globus pallidus. GLU, glutamate.

CASE 16-1

A 30-year-old man presents with dysarthria, dysphagia, stiffness, and slow ataxic gait. There is no history of schizophrenia or depression and no family history of any neurodegenerative disease.

Relevant Physical Exam Findings

●The patient scored a 20/26 on the mini-mental status exam. The patient showed increased tone in all extremities, with normal strength.

Relevant Lab Findings

●A generalized cerebral and cerebellar atrophy and a very small caudate nucleus were revealed on magnetic resonance imaging scans.

Diagnosis

●Huntington disease (chorea) is caused by a trinucleotide repeat in the gene coding for the Huntingtin protein. It is characterized by abnormal body movements and lack of coordination but can also affect

mental abilities.